Stabilizing compositions for lubricating oils

ABSTRACT

Stabilising compositions for lubricant base stocks and lubricant formulations are composed of a mixture of (a) at least one aromatic aminic amine antioxidant optionally blended with at least one hindered phenolic antioxidant and (b) at least one neutral organo phosphate or phosphite, optionally blended with at least one acid organo phosphate or phosphite. These stabilising composition mixtures are characterised by their stabilising capacity which is considerably higher than that of either the single antioxidants or the single phosphate or phosphite additives. These stabilising compositions can be used in all fields where the single components of the mixtures are generally used and where deterioration due to oxidation processes takes place.

[0001] This invention relates to stabilising compositions for lubricant base stocks and lubricant formulations.

[0002] We have unexpectedly found that mixtures of certain aromatic aminic antioxidants, optionally in admixture with certain hindered phenol antioxidants, when mixed with certain organo phosphate esters and organo phosphite esters offer unique synergy and improved performance in terms of stability when used within lubricant base stocks and lubricant formulations.

[0003] By lubricant base stocks is meant lubricants such as mineral and synthetic base oils chosen from Group I, Group II, Group III, Group IV and Group V base stocks as classified by the American Petroleum Institute, as well as natural and synthetic esters including polyol esters, more particularly, but not limited to automotive oils, circulatory oils, gear oils, greases, hydraulic fluids, turbine fluids and metal working fluids.

[0004] By lubricant formulations, is meant a lubricant base stock as described above, plus additional additives including but not limited to antioxidants, rust inhibitors, metal passivators, ashless dispersants, antiwear additives, extreme pressure additives and detergents, viscosity index improvers and antifoam agents.

[0005] According to the present invention a stabilising composition for lubricant base stocks and lubricant compositions comprises:

[0006] (a) at least one aromatic aminic antioxidant having the general formula:

[0007] wherein R¹ and R₂ are the same or different and may be H, an alkyl group with 4 to 9 carbon atoms or an aralkyl group with 8 carbon atoms and m and n are 0 to 2 but m+n is not greater than 3, either alone or optionally blended with at least one hindered phenolic antioxidant selected from those corresponding to one of the following general formulae:

[0008] wherein R₃, R₄, R₅ and R₆ are the same or different and may be an alkyl group with 1 to 4 carbon atoms and X is —S— or —CH₂— or —CH₂CH₂—S—CH₂CH₂— or —CH₂—S—CH₂— or —CH₂CH₂CO₂CH₂CH₂—S—CH₂CH₂CO₂CH₂CH₂—

[0009] wherein R₇ is an alkyl group with 6 to 20 carbon atoms; and

[0010] with (b) at least one neutral organo phosphate or phosphite optionally mixed with at least one acid organo phosphate or phosphite selected from those corresponding to the following general formulae:

[0011] (i) neutral triaryl phosphates:

[0012]  wherein R₈, R₉ and R₁₀ are the same or different and may be H, CH₃, isopropyl or tertiary butyl and m is 0 to 2;

[0013] (ii) neutral trialkyl phosphates:

[0014]  wherein R₁₁, R₁₂ and R₁₃ are all the same and are alkyl groups with 4 to 12 carbon atoms;

[0015] (iii) neutral alkyl aryl phosphates:

[0016]  wherein R₁₄ is different from R₁₅ and R₁₆ and R₁₄ is an alkyl group with 4 to 12 carbon atoms and R₁₅ is phenyl or substituted phenyl with 7 to 10 carbon atoms and R₁₆ may be an alkyl group with 4 to 12 carbon atoms or phenyl or substituted phenyl with 7 to 10 carbon atoms;

[0017] (iv) alkyl acid phosphates:

[0018]  wherein R₁₇ is an alkyl group with 5 to 12 carbon atoms and m is 1 or 2 and n is 1 or 2 but m+n is not greater than 3;

[0019] (v) neutral triaryl phosphites:

[0020]  wherein R₁₈, R₁₉, R₂₀ are the same or different and are H or alkyl with 1 to 9 carbon atoms;

[0021] (vi) neutral trialkyl phosphites:

[0022]  wherein R₂₁, R₂₂ and R₂₃ are the same or different and are alkyl groups with 1 to 18 carbon atoms.

[0023] (vii) neutral alkyl aryl phosphites:

[0024]  wherein R₂₄ and R₂₅ are the same or different and are alkyl groups with 1 to 12 carbon atoms or R₂₄ is phenyl or substituted phenyl where R₂₆ is alkyl with 1 to 9 carbon atoms.

[0025] (viii) alkyl acid phosphites:

[0026]  wherein R₂₇ may be an alkyl group with 4 to 18 carbon atoms, phenyl or substituted phenyl with 7 to 10 carbon atoms and m is 1 or 2, m is 1 or 2 but m+n is not greater than 3, and wherein the antioxidants and the phosphate(s) and/or phosphite(s) are utilised in a weight ratio from 10:1 to 1:10, preferably 1:1 to 1:5.

[0027] In one embodiment of the invention, the stabilising composition is prepared by heating the antioxidant(s) and the phosphate(s) and/or phosphite(s) for 0.2 to 6 hours at a temperature range of 40° C. to 150° C.

[0028] The treat rates of the antioxidant(s) and the phosphate(s) and/or phosphite(s) in the lubricant base stocks and lubricant compositions preferably are within the following weight ranges:

[0029] (a) aromatic amine antioxidants—0.1 to 5%;

[0030] (b) hindered phenol antioxidants—0.1 to 5%;

[0031] (c) neutral aryl phosphates—0.2 to 10%;

[0032] (d) neutral alkyl phosphates—0.2 to 10%;

[0033] (e) neutral alkyl aryl phosphates—0.2 to 10%;

[0034] (i) alkyl acid phosphates—0.01 to 5%;

[0035] (g) neutral aryl phosphites—0.2 to 10%;

[0036] (h) neutral alkyl phosphites—0.2 to 10%;

[0037] (i) neutral alkyl aryl phosphites—0.2 to 10%;

[0038] (j) alkyl acid phosphites—0.01 to 5%;

[0039] Preferably, the amine and hindered phenol antioxidants are used at 0.5 to 2.0% each. The neutral alkyl, aryl and alkyl aryl phosphates and phosphites are used at 0.5 to 4%. The acid phosphates and phosphites at 0.025 to 0.05% (when used together with the neutral phosphates).

[0040] Examples of formula I compounds are 4-tert-butyl, 4′-tert-octyl diphenylamine; 4,4′-di-tert-octyl diphenyl amine and 4,4′-di-iso-nonyl diphenylamine.

[0041] Examples of formula II compounds are 4,4′-methylene bis (2,6 ditertiary butyl phenol); 2,2′ thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxy-phenyl) propionate]; 4,4′-thiobis(2-t-butyl-5-methyl phenol); 6,6′-thiobis (2-methyl-4-t-butylphenol).

[0042] Examples of fonmula III compounds are C₇₋₉ alkyl ester of 3,5-di-tert-butyl-4-hydroxy benzene-3-propionic acid; C₁₄₋₁₆ alkyl ester of 3,5-di-tert-butyl-4-hydroxy benzene-3-propionic acid.

[0043] An Example of formula IV compounds is pentaerythritol tetra ester of 3,5 di-tert-butyl-4-hydroxy benzene-3-propionic acid.

[0044] Examples of formula V compounds are tri-dimethyl phenyl phosphate; tri-isopropyl phenyl phosphate; mono-phenyl-di (-tert-butyl phenyl) phosphate.

[0045] Examples of formula VI compounds are tributyl phosphate; trioctyl phosphate.

[0046] Examples of formula VII compounds are octyldiphenyl phosphate; dibutyl-mono-phenyl phosphate.

[0047] Examples of formula VIII compounds are dipentyl hydrogen phosphate; di C₁₀₋₁₂ alkyl-hydrogen phosphate; C₁₀₋₁₂ alkyl-dihydrogen phosphate.

[0048] An Example of formula IX is tris nonyl phenyl phosphite.

[0049] Examples of formula X are trilauryl phosphite; trioctyl phosphite.

[0050] Examples of formula XI are decyl diphenyl phosphite; didecyl monophenyl phosphite.

[0051] Examples of formula XII are dibutyl hydrogen phosphite; dioctyl hydrogen phosphite; cetyl stearyl hydrogen phosphite.

[0052] Using stabilising compositions of the invention, lubricant base stocks and lubricant formulations can have varying levels of stability dependent on:

[0053] (i) proper choice of the antioxidant(s) and phosphate(s) and/or phosphite(s) to provide for the best performance, in tenns of stability, within particular lubricant base stocks or particular lubricant formulations; or

[0054] (ii) by changing the ratio of the antioxidant to the phosphate(s) and/or phosphite(s); or

[0055] (iii) keeping the ratio of the antioxidant(s) to the phosphate(s) and/or pbosphite(s) constant while altering or decreasing the treat rate of the antioxidant(s) and phosphate(s) and/or phosphite(s).

[0056] (iv) changing the ratio of neutral phosphate to acid phosphate and neutral phosphite to acid phosphite.

[0057] In other words, the components of the mixtures of the invention, either individually or in combination, can be tailored to provide the required performance characteristics in terms of stability, in a particular base stock and/or lubricant formulation.

[0058] Embodiments of the invention will now be described by way of example with reference to the Table set out below.

[0059] The Table shows the relative oxidation stability results obtained by adding certain antioxidant(s) and phosphate(s) and/or phosphite(s) mixtures to Group III base stocks. The relative oxidation stabilities of the lubricant base stock is determined by the rotating bomb oxidation stability test (RBOT), IP test method number 229. The oxidation stability is defined as the number of minutes required to effect a reduction in oxygen pressure of 25.4 PSI or 1.75 bar when the oil and additives are heated at 150° C. in an oxygen pressurised vessel.

[0060] The results in the Table show that there is a synergistic effect (in terms of stability) when a blend of additives according to the invention is added to Group III lubricant base stocks. ASTM IP 229 ROTARY BOMB OXIDATION TEST DATA Conc Conc RBOT LIFE BASE OIL (%) ANTIOXIDANT (%) PHOSPHATE ESTER (mins) Group III Mineral oil 25 ″ 1.0 Neutral Tri Aryl Phosphate (Isopropylated phenyl phosphate) 40 ″ 1.0 Neutral Tri Aryl Phosphate (Tertiary Butylated phenyl phosphate) 22 ″ 1.0 Neutral Tri Alkyl Phosphate (Tri Octyl phosphate)) 17 ″ 1.0 Alkyl Aryl Phosphate (Octyl diphenyl phosphate) 30 ″ 1.0 Alkyl Aryl Phosphate (Iso decyl diphenyl phosphate) 25 ″ 1.0 Acid Alkyl Phosphate (C10-C12) 18 ″ 0.05 Acid Alkyl Phosphate (C10-C12) 21 ″ 1.0 95:5 Neutral Tri Aryl Phosphate (Isopropylated phenyl 20 phosphate) + Acid Alkyl phosphate (C10-C12) ″ 0.5 Butyl/Octyl diphenylamine 1088 0.5 Butyl/Octyl diphenylamine 1.0 Neutral Tri Aryl Phosphate (Isopropylated phenyl phosphate) 1250 ″ 0.5 Butyl/Octyl diphenylamine 1.0 Neutral Tri Aryl Phosphate (Tertiary Butylated phenyl phosphate) 1430 ″ 0.5 Butyl/Octyl diphenylamine 1.0 Neutral Tri Alkyl Phosphate (Tri Octyl phosphate) 1795 ″ 0.5 Butyl/Octyl diphenylamine 1.0 Acid Alkyl phosphate (C10-C12) 880 ″ 0.5 Butyl/Octyl diphenylamine 1.0 3:1 Neutral Tri Aryl Phosphate (Isopropylated phenyl phosphate) + 1415 Acid Alkyl phosphate (C10-C12) ″ 0.5 Butyl/Octyl diphenylamine 1.0 9:1 Neutral Tri Aryl Phosphate (Isopropylated phenyl phosphate) + 1811 Acid Alkyl phosphate (C10-C12) ″ 0.5 Butyl/Octyl diphenylamine 1.0 95:5 Neutral Tri Aryl Phosphate (Isopropylated phenyl phosphate) + 2068 Acid Alkyl phosphate (C10-C12) ″ 0.5 Butyl/Octyl diphenylamine 1.0 95:5 Alkyl Aryl Phosphate (Octyl diphenyl phosphate) + Acid 1967 Alkyl phosphate (C10-C12) ″ 0.5 Butyl/Octyl diphenylamine 1.0 95:5 Alkyl Aryl Phosphate (Iso decyl diphenyl phosphate) + Acid 1915 Alkyl phosphate (C10-C12) ″ 0.5 Di Nonyl diphenylamine 640 ″ 0.5 Di Nonyl diphenylamine 1.0 Neutral (Isopropylated phenyl phosphate) + Acid 833 Alkyl phosphate (C10-C12) 95:5 ″ 0.5 1:4 High molecular weight 730 phenolic (Form 4) + Butyl/Octyl diphenylamine ″ 0.5 1:4 High molecular weight 1.0 95:5 Neutral Tri Aryl Phosphate (Isopropylated phenyl phosphate) 1537 phenolic (Form 4) + Tri Aryl Phosphate + Acid Alkyl phosphate (C10-C12) Butyl/Octyl diphenylamine ″ 0.5 15:15:70 Sulphur 372 containing phenolic (Form 2) + High molecular weight phenolic (Form 4) + Butyl/Octyl diphenylamine ″ 0.5 15:15:70 Sulphur contain- 1.0 95:5 Neutral Tri Aryl Phosphate (Isopropylated phenyl phosphate) + 646 ing phenolic (Form 2) + Acid Alkyl phosphate (C10-C12) High molecular weight phenolic (Form 4) + Butyl/Octyl diphenylamine ″ 0.5 1:4 Sulphur containing 355 phenolic (Form 2) + Otcyl/Styryl diphenylamine ″ 0.5 1:4 Sulphur containing 1.0 95:5 Neutral Tri Aryl Phosphate (Isopropylated phenyl phosphate) + 908 phenolic (Form 2) + Acid Alkyl phosphate (C10-C12) 4-Octyl/Styryl diphenylamine ″ 0.5 1:4 Sulphur containing 365 phenolic (Form 2) + Butyl/Octyl diphenylamine ″ 0.5 1:4 Sulphur containing 1.0 95:5 Neutral Tri Aryl Phosphate 755 phenolic (Form 2) + (Isopropylated phenyl phosphate) + Butyl/Octyl diphenylamine Acid Alkyl phosphate (C10-C12) 

1. A stabilising composition comprising a mixture of: (a) at least one aromatic aminic antioxidant having the general formula:

 wherein R₁ and R₂ are the same or different and may be H, an alkyl group with 4 to 9 carbon atoms or an aralkyl group with 8 carbon atoms and m and n are 0 to 2 but m+n is not greater than 3, either alone or optionally blended with at least one hindered phenolic antioxidant selected from those corresponding to one of the following general formulae:

 wherein R₃, R₄, R₅ and R₆ are the same or different and may be an alkyl group with 1 to 4 carbon atoms and X is —S— or —CH₂— or —CH₂CH₂—S—CH₂CH₂— or —CH₂—S—CH₂— or —CH₂CH₂CO₂CH₂CH₂—S—CH₂CH₂CO₂CH₂CH₂—

 wherein R₇ is an alkyl group with 6 to 20 carbon atoms; and

 with (b) at least one neutral organo phosphate or phosphite optionally mixed with at least one acid organo phosphate or phosphite selected from those corresponding to the following general formulae (i) neutral triaryl phosphates:

 wherein R₈, R₉ and R₁₀ are the same or different and may be H, CH₃, isopropyl or tertiary butyl and m is 0 to 2; (ii) neutral trialkyl phosphates:

 wherein R₁₁, R₁₂ and R₁₃ are all the same and are alkyl groups with 4 to 12 carbon atoms; (iii) neutral alkyl aryl phosphates:

 wherein R₁₄ is different from R₁₅ and R₁₆ and R₁₄ is an alkyl group with 4 to 12 carbon atoms and R₁₅ is phenyl or substituted phenyl with 7 to 10 carbon atoms and R₁₆ may be an alkyl group with 4 to 12 carbon atoms or phenyl or substituted phenyl with 7 to 10 carbon atoms; (iv) alkyl acid phosphates:

 wherein R₁₇ is an alkyl group with 5 to 12 carbon atoms and m is 1 or 2 and n is 1 or 2 but m+n is not greater than 3; (v) neutral triaryl phosphites:

 wherein R₁₈, R₁₉, R₂₀ are the same or different and are H or alkyl with 1 to 9 carbon atoms. (vi) neutral trialkyl phosphites

 wherein R₂₁, R₂₂, and R₂₃ are the same or different and are alkyl groups with 1 to 18 carbon atoms. (vii) neutral alkyl aryl phosphites:

 wherein R₂₄ and R₂₅ are the same or different and are alkyl groups with 1 to 12 carbon atoms or R₂₄ is phenyl or substituted phenyl where R26 is alkyl with 1 to 9 carbon atoms. (viii) alkyl acid phosphites:

 wherein R₂₇ may be an alkyl group with 4 to 18 carbon atoms, phenyl or substituted phenyl with 7 to 10 carbon atoms and m is 1 or 2, n is 1 or 2 but m+n is not greater than 3,  and wherein the antioxidants and the phosphate(s) and/or phosphite(s) are utilised in a weight ratio from 10:1 to 1:10.
 2. The stabilising composition in accordance with claim 1 wherein the antioxidant(s) and the phosphate(s) and/or phosphite(s) are utilised in a weight ratio from 1:1 to 1:5.
 3. The stabilising composition in accordance with claim 1 or claim 2 which has been prepared by heating the antioxidant(s) and the phosphate(s) and/or phosphite(s) for 0.2 to 6 hours at a temperature between 40° C. and 150° C.
 4. A lubricant base stock or lubricant composition stabilised by the stabilised composition of any one of claims 1 to
 3. 